A slang term combining Hebrew and English to describe someone who is slightly or partially "off" mentally or behaviorally, not fully meeting a label but showing characteristics of it. "Avak" comes from the Hebrew term meaning "dust" or "partial" and implies an indirect or lesser form of something.
Bochur pacing during a shidduch reference call
“He’s not toit meshuga, you chap? I wouldn’t call him completely retarded. He’s avak retarded, yeah?”
In this context, "avak retarded" suggests that a person is not entirely mentally deficient but displays traits that could be seen that way.
He was being avak retarded when he tweeted:
Christmas Robin Hood’s Men
🤝
Being Merry